docs: def pixel_range(self, waverange, waveunits=None, round='round'):
          """Returns the number of wavelength bins within ``waverange``.
  
          .. note::
  
              This calls :func:`pixel_range` with ``self.binset`` as
              the first argument.
  
          Parameters
          ----------
          waverange, round
              See :func:`pixel_range`.
  
          waveunits : str, optional
              The units of the wavelengths given in ``waverange``.
              If `None` (default), the wavelengths are assumed to be
              in the units of ``self.waveunits``.
  
          Returns
          -------
          num : int or float
              Number of wavelength bins within ``waverange``.
  
          Raises
          ------
          pysynphot.exceptions.UndefinedBinset
              If ``self.binset`` is `None`.
  
          """
          # make sure we have a binset to work with
          if self.binset is None:
              raise exceptions.UndefinedBinset('No binset specified for this bandpass.')
  
          # start by converting waverange to self.waveunits, if necessary
          if waveunits is not None:
              waveunits = units.Units(waveunits)
  
              if not isinstance(waverange,np.ndarray):
                  waverange = np.array(waverange)
  
              # convert to angstroms and then whatever self.waveunits is
              waverange = waveunits.ToAngstrom(waverange)
  
              waverange = units.Angstrom().Convert(waverange, self.waveunits.name)
  
          return pixel_range(self.binset, waverange, round=round)